The present invention generally relates to methods and apparatuses for delivery of fluids in a processing system used for the fabrication of integrated circuits and flat panel displays. Specifically, the present invention relates to methods and apparatuses for heating fluid delivery lines in a vacuum processing system in order to heat the fluid flowing therein and for containing fluid leaked from the fluid delivery lines.
Vacuum processing systems for processing 100 mm, 200 mm, 300 mm or other diameter wafers are generally known. Typically, such vacuum processing systems have a centralized transfer chamber mounted on a monolith platform. The transfer chamber is the center of activity for the movement of substrates being processed in the system. One or more process chambers and load lock chambers mount on the transfer chamber, and a transfer chamber robot mounts in the middle of the transfer chamber to access each of the process chambers and load lock chambers to transfer a substrate therebetween. Different process chambers perform different processes on the substrates. For example, a physical vapor deposition (PVD) chamber or a chemical vapor deposition (CVD) chamber may deposit a layer of material, such as a conductor or an insulator, onto the surface of the substrate; or an etch chamber may remove a layer of material from parts of the surface of the substrate; or an ion implantation chamber may implant ion dopants into the substrate; or a pre-clean chamber may remove a layer of the substrate contaminated with oxides; or a thermal processing chamber may heat a substrate to cure or anneal the substrate after a previous process. In fact, it is not uncommon for a manufacturer of semiconductor processing systems to provide over twenty different types of process chambers. Access to the transfer chamber from the clean ambient environment is typically through the load lock chambers. The load lock chambers may open to a very clean room, referred to as the white area, or to a substrate handling chamber, typically referred to as a mini-environment, for transferring substrates in a very clean environment at atmospheric pressure from pods seated on pod loaders to the load lock chambers.
Each type of process chamber typically performs one specific step or series of steps in the overall fabrication of integrated circuits or flat panel displays. For example, some types of process chambers specifically deposit one particular material onto the surface of the wafer. Other types of process chambers specifically etch away a particular layer from the surface of the wafer. Still other types of process chambers specifically implant a particular ion into the wafer.
Many of these processes require that certain gases or liquids be delivered to the process chamber to perform the process. These gases and liquids are commonly called process fluids and are delivered to the process chambers through fluid delivery lines from sources of the fluids in the manufacturing plant. For example, a chemical vapor deposition process of copper may require cupraselect, a metal organic compound, be provided as a precursor in the process. Another process may use dimethylaluminumhydride (DMAH) to perform chemical vapor deposition of aluminum. Yet another process may use tetrakisdimethylaminotitanium (TDMAT) to deposit a film of titanium nitride on a wafer. Still another process may use barium and strontium precursors to deposit a film of barium strontium titanate (BST). The process fluids are typically converted into a gaseous state by vaporization, bubbling or other appropriate process to deliver a vapor of the process fluid to the process chamber.
Many of these process fluids must be maintained within a specific temperature range while flowing through the fluid lines to prevent deposits along the path. Also, many of these process fluids are toxic, pyrophoric, corrosive, or otherwise hazardous, so special safeguards must be employed to prevent leakage of the process fluids into the ambient air.
Those process fluids that must be maintained within a particular temperature range while flowing through the fluid lines, may need to be in a gaseous state in order to flow properly through the fluid lines or to enter the process chamber in the proper concentration or condition for processing. Condensation of the process fluids may cause a loss of controllability or repeatability of the process, including a loss of accurate delivery of the process fluid from one wafer to the next or a loss of control over the amount of material deposited on a single wafer. Thus, these process fluids must be maintained above their vaporization temperature, so that they remain gaseous. Additionally, many of these process fluids are molecular compounds which may decompose, or chemically breakdown into their constituent elements or other molecules, above a certain temperature. Thus, these process fluids must be maintained below their decomposition temperature.
Some of these process fluids may have a fairly wide window between their vaporization temperature and their decomposition temperature, so that maintaining the fluid lines and the process fluid within the required temperature range may be fairly easy. Other process fluids, however, may have a narrow window between their vaporization temperature and their decomposition temperature, so that maintaining the fluid lines and the process fluid within the required temperature range may require a very tightly controlled delivery process in order to ensure that the temperature of the entire fluid delivery line does not vary. For example, cupraselect has a vaporization temperature of about 75xc2x0 C. and a decomposition temperature of about 85xc2x0 C. Thus, cupraselect has a very narrow temperature range within which it must be maintained for proper operation of a process that uses cupraselect. By comparison, DMAH has a vaporization temperature of about 40xc2x0 C. and a decomposition temperature of about 180-200xc2x0 C., and TDMAT has a vaporization temperature of about 50xc2x0 C. and a decomposition temperature greater than about 300xc2x0 C. Thus, these compounds present a fairly wide temperature range which is considerably less difficult to maintain than that of cupraselect.
FIG. 1a shows a simplified schematic of a process fluid source 10, a process chamber 12 and the delivery system in between. The fluid delivery system heats the process fluid in a hot box 14 next to the source 10 prior to flowing the process fluid through the fluid lines 16 to the process chamber 12. One or more fluid lines (not shown) are attached to the process fluid source 10 and connected to a system of valves (not shown) for regulating the flow of the process fluid. These fluid lines and valves are typically housed within the hot box 14. The hot box 14 is a closed heated environment for heating the regulating valves and the fluid lines that are immediately adjacent to the fluid source 10. Thus, the process fluid enters the fluid lines 16 for delivery to the process chamber 12 within the appropriate temperature range. The hot box 14 does not heat the fluid lines 16 that deliver the process fluid to the process chamber 12.
Since there may be several feet of fluid delivery line between the process fluid source and the process chamber, the fluid delivery line may also have to be heated. Otherwise, the process fluid may condense within the fluid lines before it reaches the process chamber and disrupt the proper functioning of the process. FIG. 1b shows a portion of a fluid delivery line 16 illustrating the means for heating the fluid line 16 between the hot box 14 and the process chamber 12. The fluid line 16 has an angled portion 18 and a section 20 that does not have the same diameter as the rest of the fluid line 16. Section 20 may be a fitting or a joint connecting two portions of the fluid line 16, or a valve section controlling the flow through the fluid line 16, or an intersection of more than one fluid line 16, or some other line section disposed in the fluid line 16 that presents an interruption in the contour of the outer surface of the fluid line 16.
A length of heating tape 22 is adhesively attached to the outer surfaces of each of the sections of the fluid line 16 between the hot box 14 and the process chamber 12. The heating tape 22 is typically a semi-flexible resistive tape that is heated with an electrical current. The heating tape 22 heats each section of the fluid line 16 in order to maintain the fluid line 16 and the process fluid within the appropriate temperature range. FIG. 1b shows the heating tape 22 attached longitudinally down the length of the fluid line 16. The heating tape 22, however, may be wrapped around the fluid line 16 in other manners as well.
A problem with the heating tape 22 is that gaps 24 frequently occur between the heating tape 22 and parts of the fluid line 16, so there is no contact therebetween at those locations. Cool spots can occur within the fluid line 16 at the location of these gaps 24, and hot spots can occur where the heating tape 22 may be concentrated. The variance in temperature may be +/xe2x88x9220xc2x0 C., and even in a well-assembled system may be +/xe2x88x9210xc2x0 C., very significant variances for a process gas such as cupraselect, as discussed above. If the cool spots are below the vaporization temperature of the process fluid, then the process fluid will form condensation at these cool spots inside the fluid line 16. Thus, the flow of the process fluid may be disrupted, and the system may lose control and repeatability of the performance of the process. If the operator of the system attempts to compensate for the cool spots by increasing the temperature of the heating tape 22, then the system may run the risk of exceeding the decomposition temperature of the process fluid, and the process fluid may break down into its constituent elements or other molecules, which will not perform the required process in the process chamber 12.
Another problem with the heating tape 22 is that many heat-trace applications in chemical vapor deposition rely on temperature gradients to prevent condensation throughout the fluid line 16. With the conventional heating tape 22, the temperature gradient can be created only with discontinuous steps through the fluid line 16. The discontinuous steps require separate controls for each step. A continuous temperature gradient with no additional controls would be preferable.
Those fluid lines that are delivering process fluids that are toxic, pyrophoric, corrosive, or otherwise hazardous should have a secondary containment means for capturing leaked fluid. The captured fluid needs to be safely contained and delivered to a facility for extracting or disposing of the hazardous material typically in the area of the fabrication facility commonly referred to as pump alley or in the gray area. Conventional secondary containment methods provide containment of only the volume in the straight sections of the fluid line and do not cover the fittings, joints or other discontinuities between the straight sections. However, leaks are more likely to occur at a fitting, joint, intersection, valve or other discontinuity in the fluid line than in the straight sections. Thus, conventional secondary containment methods have been inadequate in covering the entire fluid lines to adequately contain and remove hazardous fluids at the locations most likely to experience a leak.
A need, therefore, exists for a secondary containment method that covers all of the sections of the fluid line and for a line heating means that heats the fluid line uniformly from the fluid source or hot box to the process chamber.
A vacuum processing system has a process chamber mounted to a centralized transfer chamber and a primary fluid line for delivering a process fluid to the process chamber from a source of the process fluid. A secondary containment line surrounds the primary line for substantially all of the length of the primary line. A gas, or fluid, such as nitrogen, flows through the secondary containment line and around the primary containment line. This gas purges any of the process fluid that may have escaped from the primary fluid line. The purge gas carries the process fluid to an appropriate handling facility for safe disposal of the process fluid. The purge gas may also be heated. The heated gas heats the primary line, and the process fluid as it flows therethrough, and flows away any leaked process fluid. Since the heated gas is constantly flowing around the primary line, the heat is distributed evenly along each section of the primary line and the joints therebetween.
The heated gas may lose heat through the shell of the secondary containment line as the heated gas flows away from its inlet port to its outlet port. Thus, the process fluid will be heated through a temperature gradient. The gradient may be increasing or decreasing depending on the placement of the inlet port and the outlet port for the heated gas. Alternatively, a heating element, such as heating tape, may be wrapped around the secondary containment line to add additional heat to the heated gas. As the heated gas loses heat as it flows through the secondary containment line, the heating element may add heat so that there is no temperature gradient, or so that there is an increasing temperature gradient. Thus, the temperature range experienced by the process fluid may be very tightly controlled.
The shell of the secondary containment line includes a series of interlocking sections that conform to the shape of the fluid delivery lines. The straight sections are essentially cylindrical in shape with openings at both ends, but with a longitudinal opening extending between both end openings. A section of secondary containment line fits loosely over a partially assembled primary containment line through the longitudinal opening. Another section of secondary containment line fits around the primary containment line on the opposite side from the first section and slides or snaps through the longitudinal opening of the first section. Thus, the two sections together form a fully cylindrical pipe section assembly around the primary containment line. Any cracks or holes between sections may be covered with tape or filled with caulk. Support braces placed every few inches along the primary containment line serve as spacers to separate the secondary line shell from the primary line, so that the heated gas has space to flow all around the primary containment line.
The various secondary line section assemblies covering the various fitting and other discontinuities in the primary line are formed with the same basic structure as the straight section assemblies. For example, an angled section assembly is formed from essentially two pieces of straight section attached at an angle with their longitudinal openings facing each other on the acute side of the angle. Two regular straight sections cover the longitudinal openings of the angled sections. An intersection assembly includes two regular straight sections, one of which has a circular opening cut on a side opposite its longitudinal opening and fitted with a short, fully-cylindrical piece to form a T-section. The other straight section inserts into the longitudinal opening of the T-section, and the short cylindrical piece may receive another section assembly. A valve section assembly for covering a valve in the primary line includes the same or similar T-section as for the intersection assembly, but with a cylindrical cover over the short cylindrical piece that can be removed to access the valve. Additionally, a small hole in the cover provides a pneumatic control line input.
In another embodiment, a heat trace has a shell enclosing the process fluid delivery line and conforming to the outer surface of the fluid delivery line so that it is in thermally conductive contact therewith. The shell is formed from two half-shell sections with flanges at their mating surfaces for applying a fastener to hold the two half-shell sections together. Each half-shell section is sufficiently thick for a series of longitudinal holes to be formed therethrough. A plurality of cable heaters, such as resistive wires, disposed through some or all of the longitudinal holes, extend along the length of the heat trace. A controller provides precise temperature control for the cable heaters. Optionally, one or more temperature measurement devices, such as thermocouples, are disposed through one or more of the longitudinal holes at periodic locations to provide temperature feedback readings to the controller, so the controller can adjust the temperature of the cable heaters to a desired temperature. This embodiment can provide very tight control over the temperature of the fluid delivery line.